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2016 Limited AC Compressor Won't Engage Except When Jumped


Swifty Morgan

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I have a 2016 Explorer Limited. The other day, the AC started blowing warm. When I jump the relay at the fuse block, the compressor turns on, and the AC works fine. Otherwise, the compressor will not run. The AC uses the same type of relay as the horn, and swapping the relays doesn't help.

I shot a little refrigerant into the car while the compressor was running. I didn't have a gauge, so I was afraid to overdo it. I figured I would shoot enough in there to make sure the problem wasn't low refrigerant. The compressor still will not run unless it's jumped.

Any ideas? I would like to get the right tools, evacuate the system, charge it, and see how things go, but if the compressor won't run, I guess I'll have to pay a mechanic.
 


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03WIExplorerLtd

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Don't add freon unless you have a gauge. It can make things worse.
 




JAPeterson

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I'm sure that there is a shop around you that will do a free AC test. Just don't tell them that you plan on fixing it yourself.

However I believe that there are a few things on a vehicle that are best left to the experts on it, the AC is one of them.
 




peterk9

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Is there power going to the relay? Sounds like that might be the problem. Position #3 in the engine bay fuse block is for;
A/C clutch control relay coil.
VACC.
Active grill shutters.

#38 appears to be the relay; A/C compressor clutch relay.
Even though you can start the compressor by jumping the relay, I wonder if it could still be bad?

Peter
 
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Swifty Morgan

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Thanks for the replies. Swapping the horn relay into the clutch relay socket doesn't fix the AC, so the relay must be fine.
 




peterk9

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Have you confirmed that there is power to the relay?
 




Swifty Morgan

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Yes. The clutch works fine when the relay is bypassed.
 








runningonfords

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Quickly go look above your driver's side muffler at the gray a/c lines there. Are they green with leaking refrigerant?
 




CDW6212R

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Yes. The clutch works fine when the relay is bypassed.
I believe the AC relay is powered by the LPS wiring, but check that to be sure it is. If the signal is getting to that AC relay, than the power(current) isn't enough to trigger the relay. remember too that the AC compressor is run by the main circuit, and shut down by a different circuit(trigger wire). That's why it's call the WOT relay, it passes current all the time, but the trigger wire is from the TPS signal telling the system to shut off the compressor.

My last 91 Lincoln had an issue with the compressor shutting off, first after a minute, and then less and less time. The main EATC unit runs full current in those, and with old age the current dropped, resistance inside the EATC was the problem. I didn't want o pay to have it fixed then, and now no one does that any longer. I added a relay instead, the old AC wiring signal is enough to trigger a relay. So the new relay allowed me to leave the old EATC in place, and work.

All fragile electronics should be made to not have high current control inside of them, relays should be used to lengthen the lifespan of those precious parts. It's no big deal when the vehicle is under ten years old. Wait till it's 20 years old and see how things change.
 




Swifty Morgan

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Thank for the replies. The refrigerant level is fine. There is nothing leaking.

Because the relay is good, I know something is preventing it from getting a signal to close the switch. The fuse is fine.

I don't think there's anything wrong with the cabin electronics, because the system reacts normally to input, apart from starting the compressor. You can switch from AC to heat and so on.
 




CDW6212R

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You missed the point, another member also pointed to it. You seem to have a current at the relay, power current, not the trigger current. Unless the newest Fords also have an extra relay to power the compressor, the trigger wire is just to shut it down(it's a NC relay(passes current normally).

I'm not familiar with the latest car wiring, I said that. Almost all Fords used to have full current going to the compressor, with the pressure switches and the WOT relay in line with that, coming from the dash. Each of those is to cut the current from turning on the compressor, without them the compressor will run(jumping/bypassing each of those).

You said you could bypass the relay to run the compressor, that is a good sign to help with. The power current is coming through the pressure switches(LPS and HPS), to the relay. Not being sure, I'm guessing the AC relay is the same as all older Fords, it's a WOT relay, it only triggers at WOT, to shut off the compressor. So the relay is normally closed, the terminals used are not the normal four, one is the NC terminal being fed.

I am stating these details so you can figure it out based on how Fords have been for decades, not because I know what the problem is. But knowing how the circuits work should help you or anyone with similar issues, to figure it out.
 




Swifty Morgan

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I know I have no trigger current. But why?

I should also add that no codes pop up when I connect an Actron scanner.

Another thing: I started getting warnings the car was overheating. I jammed a water bottle in the radiator shutters, and the problem went away. I noticed that sometimes the temperature reading changed instantly, as though a sensor were screwed up. Don't know if this is relevant.
 
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CDW6212R

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Go back to the relay and identify which terminals are being used. That might be easy given the original relay, there should be scratches on the used terminals, and one will be unused. If you look at what are being used, it should be possible to determine if the trigger wire is for the NC terminal, or for the NO terminal. Of the five typical relay terminals, three are not for high current, not the main two terminal path. Of those three, one is ground, and one of the other two is usually a trigger power terminal. The ground can be used to trigger a relay also, but it isn't with the AC circuit.

If the relay is being used as a NC circuit(the terminal going to the compressor), then it is a typical WOT relay circuit. The power goes through it constantly, it is not triggered on. Only if it is a NO relay(the terminal going to the compressor), will the trigger wire be used to feed the power to the compressor. The source of the trigger wire is to power the compressor, or to shut it off.
 
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Swifty Morgan

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This is a 4-prong relay (8T2T-CA). The front two prongs, with relation to the car's position, supply power to turn the compressor on. It is impossible to determine which prong goes to the compressor without removing the fuse box or getting someone to crawl under the car and help do some kind of continuity test. The compressor is under the engine, a long way from the fuses and relays. Presumably, one of the remaining prongs goes to ground, and the other goes to the compressor.

The relay's switch is open except when the compressor is running, so no current goes to the compressor unless the relay is closed. If the compressor worked when the switch was open, then bypassing the relay would turn the compressor off.

The relay works just fine. The problem is somewhere else. The signal that closes the relay is not coming.

I would like to bypass the low pressure switch, but I don't know where it is or how to do it. I have also read that the evaporator sensor can go bad, and that Ford manufactured this car so replacing it requires a whole new evaporator and an outlay of maybe $800.
 




CDW6212R

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Okay, so it sounds like that relay is solely to turn on the compressor, and there is a separate one elsewhere to disable it under WOT. That was my confusion, I hope I didn't confuse anyone else.

The LPS is easy to find, the HPS also, they are located on the AC lines/hoses running from the compressor to the condenser and evaporator or drier. There should be power at those connectors when the AC is turned on, or specifically any time the AC power control is on and the VENT is not selected. The compressor runs all the time except during VENT, and when the controls are off.

So when you said jumping past the relay ran the compressor, you meant you jumped from a direct power source like the battery? I thought you were jumping the AC circuit power past the relay.

Look at the relays themselves, virtually all of them have a schematic diagram on them. That will identify the main power wires, #30 being the output terminal, which should lead to the compressor. The opposing terminal should be the main power terminal, presumably coming from a main power source, a fused circuit at the Power Distribution Box. You could tack that wire, and if the relay is being triggered for the compressor, than the trigger wire terminal is what should lead back to the HPS, LPS, and the AC control unit. In older relays the main power wires were large terminals, and the smaller terminals were the trigger wire circuits.

Testing the female connectors(gently) down in the PDB should help to point to the issue. Looking at the relay schematic on each should guide you to which each is for. One will show no resistance to the compressor, one to main power, one to the HPS connector, and one to some form of ground.
 




runningonfords

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Thank for the replies. The refrigerant level is fine. There is nothing leaking.

Because the relay is good, I know something is preventing it from getting a signal to close the switch. The fuse is fine.

I don't think there's anything wrong with the cabin electronics, because the system reacts normally to input, apart from starting the compressor. You can switch from AC to heat and so on.
I'll restate the obvious here. If you don't own any A/C gauges, then how do you know your refrigerant level in the system is fine? Generally, "I don't see any leaks" is an insufficient indicator to arrive at this conclusion.
 




Swifty Morgan

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I'll try to be systematic.

1. I have already figured out what the relay's pinouts are. The pins toward the front of the car are connected to the switch, and the two at the rear run the solenoid. The relay is fine.

2. When I say I jumped the relay, I mean I did what the relay does when the switch is closed. I connected two sockets which go to the switch inside the relay. The effect is like closing the switch. When I do this, the compressor runs normally.

3. I ran the AC while probing the relay socket, and there was no voltage to the solenoid side of the relay, so no signal is going to the solenoid to close the switch. In other words, the car is not trying to close the compressor clutch. I don't think it's the WOT sensor, because that causes other problems. I am wondering if it's the low pressure sensor or the evaporator temperature sensor.

3. I have checked the refrigerant level with a gauge since starting the thread, and it says it's fine.

I don't have a Helm manual, so finding out what goes where is not easy. There is a connector on the low side of the system near the front right fender and the radiator, up high. It has three wires. I managed to find about 5V on one wire. Playing with this connector (bypassing things) does not turn the compressor on. It looks like this wire runs back to the fuse box, but I can't see under the box, so I don't know where it ends. I don't know what this connector is supposed to be connected to. There is a socket for it, and the socket is connected to the low pressure side, but that's all I know. If there is a switch under it, I wouldn't know.
 




CDW6212R

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Very good, you are saying the trigger signal going to the relay isn't there or large enough to trigger the relay. You might also verify the other matching terminal is a good ground, the trigger wire goes through the relay circuit to that ground wire. If that wire doesn't lead to ground, that also would stop the relay from functioning.

So the trigger signal is not reaching the relay you think, you should be able to check that current at the LPS, and the HPS, and back at the dash control if you have the pinout diagram for it. I'd check the LPS first, test the resistance from each of the terminals on it, that should be very low to allow current to pass, but only when the engine is running(low freon or engine off would open(the contacts) that LPS).
 


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Swifty Morgan

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So where are these switches? The compressor itself is buried under the car like an inoperable brain tumor.
 




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